Application of video expander in solving video interference of elevator

Application of video expander in solving video interference of elevator

Overview In the TV monitoring project, the interference of the internal camera of the elevator is a common problem, and it is also one of the most difficult problems to be solved by the engineering business. Everyone helps.

1. Cable Selection in Elevator Monitoring In elevator monitoring, since the elevator is moving, the wiring method is different from the fixed-point monitoring of the pipe (slot) wiring method, and the selection of cables also requires a higher Mechanical strength, often engineering companies pay attention to the mechanical strength of the cable in wiring, ignoring its video transmission characteristics.
Because the elevator room is a small space that is almost closed, and there are many other control, lighting, fan and other cables in the elevator, this also increases the difficulty of wiring the video cable. Therefore, the following principles should be followed in the selection of cables.
1. To meet the tensile strength: half of the elevator cables are used for extension. The high-rise elevators can reach up to more than 1,000 meters, and the weight of the more than one hundred meters of cable is nearly 100 kilograms, so the cable must have sufficient tensile strength. Now there are special cables for self-supporting flat compound elevators on the market. This kind of cable combines video cables, power lines, data lines and steel strands into a flat ribbon cable, so that the tension of the whole cable Bearing by the steel strand, the tensile strength is greatly improved, and the cable will not be broken during the operation of the elevator.
2. Good electrical parameters: because the cable moves up and down with the elevator in the elevator, there is always a section in the middle of the cable that will be bent and deformed by gravity, which will cause the impedance characteristics of the cable to change, and the poor quality cable will deform after being stressed The coefficient is large, and after the impedance mismatch, the video attenuation naturally increases, the video signal-to-noise ratio decreases, and the image is easily interfered.
3. Choose the shielded cable with thick wire diameter as much as possible in the selection of the cable, so as to prevent the "invasion" of the interference signal.

2. Monitoring cable wiring skills in elevator monitoring In elevator monitoring wiring, the method of bundling with other cables is often used, because the AC signal in other cables leaks out through the transmission cable, and the video cable and its long-distance parallel bundling are equal to one The secondary "antenna" will couple in the interference signal, so the wiring length should be as short as possible in parallel with other cables. If possible, the video cable can be fixed at the middle point of the elevator shaft and led from other channels (cable shaft) Back to the main control room, this can avoid cable coupling interference, and also ensure the freedom of the cable.
In conditional projects, the control and lighting cables used in the elevator can be shielded to reduce external radiation and avoid video interference.

Third, the high-frequency interference of elevator frequency conversion speed control basically uses AC frequency conversion speed control technology in the elevator, and the frequency converter itself has strong high-frequency parasitic interference. According to the actual measurement results, the frequency converter radiates bandwidth It is a 0 ~ 10 MHz interference signal with strong amplitude. This interference signal can enter the video surveillance system through the power line and space radiation and interfere with the video image. This source of interference is the main reason why elevator video surveillance is susceptible to interference, and it is also the most difficult problem to solve.

Four. Interference of power supply and other factors In elevator monitoring, the camera power supply is best from the centralized DC power supply in the main control room. If the power supply cannot be directly supplied, choose to draw power from the lighting in the elevator car, but most elevators currently use elevators. The internal lighting is all fluorescent lighting. This type of lamps all use electronic ballasts. When the electronic ballasts work, they will also produce a strong AC parasitic interference output.

Fifth, elevator interference avoidance and solutions The main causes of elevator video interference have been analyzed in detail above, only to find out the cause of interference, interference problems can be solved. Solve the elevator interference should mainly start from the following points.

1. Choose a video cable with small attenuation coefficient, good shielding performance and high tensile strength, which can improve its own anti-interference ability and reduce video attenuation.

2. Reasonable wiring: Reasonable wiring can effectively avoid the "coupling" of interference signals through the cable, minimize the parallel binding distance with other cables, and keep the video cable away from interference.

3. Power interference is also an important source of interference for video signals. Therefore, it is necessary to use a power supply with a small ripple to prevent power interference or use centralized power supply in the computer room to avoid power interference. If it is not possible to determine where the interference signal was introduced into the system, first determine whether it is power interference, find a battery, and directly supply power to the camera. If the interference is eliminated, it proves to be power interference, and if it cannot be eliminated, it proves to be intrusive interference in the transmission cable.

Sixth, the anti-interference principle of the video expander The above-mentioned methods are all working in the 0 ~ 6MHz video baseband transmission. These methods are often invisible and intangible to engineering companies. The solution is not Very smooth, and most of the interference problems were discovered during the debugging process after the system wiring was completed, so can you use a simple method to eliminate interference problems?
Beijing Stellar ’s ST-501 video expander is designed for the above problems. Its transmission principle is to skillfully bypass the interference frequency band and move the video signal once to a frequency of about 40 MHz. DSP digital processing and carrier communication technology, after the image signal is transmitted to the main control room and then restored to 1VP-P video signal, without making a fuss in the interference band. This effectively solves the "coupling interference, radiation interference".
Another major advantage of the video expander in the anti-interference of the elevator is that it is simple to install and debug. Add a DC12V power supply to the video expander transmitter and receiver, connect the camera to the VidioIN of the video expander, and then output it to the F block of 38MHZ intermediate frequency Video expansion receiver F block input, and then video output to the monitor. There is no need to change the original cable and wiring structure.